Synchronism corrector for telegraph systems



E. R. sHENK 2,258,152

SYNCHRONISM CORRECTOR FOR TELEGRAPH SYSTEMS Filed March 30, 1940 2 Sheets-Sheet 1 Oct. 7, 1941 Oct. 7, 1941. E. R. sHENK I SYNCHRONISM CRRECTOR FOR TELEGRAPH SYSTEMS Filed March 30, 1940 2 Sheets-Sheet 2 NB om @MSR @2G53 INVENTOR. .El/g5 R. SHENK ,enel The invention v and both front and able under ordinary working cases, however, the A an 'element in combination with other features byH Patented Oct. 7.19.4? l

UNITED *STATES 4Pa'llalv'i oFFlcs sYNcnnoNlsM coaasc'ron ron. TELE- Gaarn SYSTEMS Eugene R. Shenk,

Brooklyn, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application Mei-c so, 194e. Serin No. 326.903

, 6 Claims. (Cl. P18-89.5)

' This invention relates to improvements in a phase corrector for synchronizing the operating equipment at the receiving end of a telegraph system with thel equipment at the transmitting has particular application to the maintenance of a receiving distributor in phase synchronism with the speed of transmission of telegraph signals. The signals are caused to produce a corrective action whenever the speed of the receiving distributor departs from that of the transmitting distributor.

multiplex telegraphy. and to provide means for measuring two time intervals, one of which elapses between the front edge of a marking signal and a local impulseproduced in accordance with the receiving distributor phase and as near as possible to the normal center of a. time allotment for reception of a dot unit impulsa; and to By a gradual process of evolution phase cor- Y p time intervals were, therefore, derived, the durations of these intervals being differentiated from Richard E. Mathes in his one another in such manner as-toproduce the l necessary phase correction of a distributor.

The device disclosed in the instant application has for its objctto' improve upon the arrangements heretofore known. I have found that cervrtain simplifications in the corrector circuit may Vbe made, and that the operating of the phase 'corrector may be made more dependconditions. 7-

In my copending application Serial No. 326,902, wfiled on the same date of this 'applicationJ have disclosed another embodiment of a phase 'corvrector for a telegraph system wherein the two aforesaid time intervals to be differentiated are derived in a somewhat different manner from*k that which isuisclcsed 1n this application. .In the two-embodiments illustrated, however, I .have indicated certain similarities of circuit arrangements, particularly respecting the use of an electronic oscillator for producing a synchronized baud frequency output whereby any telegraph distributor maybe maintained -in synehronism with the incoming signals.

oscillator is claimed onlyas which the two disclosures are patentabiydistin- '1tnen object of my mvenacn te provide c dependable circuit t for phase correction of a distributor, such as characteristics compare this time interval with another time interval which immediately follows the first time inter-v9.1 aus extends to the beck edge er the marking signal.

It is lanother object of my invention to provide a phase correction system wherein use is made of a pulse wheel for derivation of a single train of local impulses, whose phase is to be maintained at the baud center of each marking impulse of dot unit length.

Other objects and advantages of my invention will be made apparent in the following detailed description wherein reference is-made to the accompanying drawings, in which e Figure l shows diagrammatically a preferred circuit arrangement including the essential elements in combination for carrying out the invention; and Y Figs. 2 to 7 inclusive are .plots of'electric impulses which occur. in various parts of the circuit ement. These plots are ally drawn to the same horizontal time scale in order toshow the correlation of essential operations.

v In the following description I have adopted a system of references to the several parts in com.

bination as follows: All references bearing the initial V will ,be vunderstoodtofrepresent discharge tubes either of the vacuum type or of the gas-nlledl ionization type. The 'gas-filled4 tubes are,.. however, conventionally shown in Fig. 1 by means. of 'a black spot in the discharge zone. Resistors are referenced RI, RL-RS, etc., while capacitors are referenced Ci, C2. C3, etc. For

.- the sake of brevity, the various tubes. resistors In the .respective A nais wherein the front edgeof4 a lmarking ele- 'used in 55 'may be more readily are first referred tol forexplaining operation which are to be' performed.

and capacitors will at vtimes be mentioned by their identifying symbols alone.

. In order that the requirements corrector vcircuit arrangement shown in Fig, 1 understood, Figs.- 2 m 'I Fig. Z'shows'a time plot of an incoming train yof signals. -Thetone frequency signals are im pressed across the transformer 2, duringmaiking periods. Fig. 2'shows such a of-Si8- mentismecchccsedesmnsteunwhilctnencck edge thereof is denmtcdvn. B anu r of thevphasethe steps oi' the tone frequency is suppressed to represent a spacing period.

Referring to Fig. 3, I show the result of rectifying the keyed tone frequency signals. A curve of square wave formation is produced by rectication, the conductive times of the rectifier VI being indicated by the wave crests, while nonconductive times are indicated by wave valleys.

Fig. 4 shows a plot of conductive and non-conductive times for tubes V2, V8, VII, VI4 and V15. The marking signal commences at points marked M, at which moments a resulting voltage change across resistor RI I produces ionization of V4 and extinction of V6.

Fig. 5 shows a curve of impulse generation locally by means of an impulse wheel having means for varying the magnetic ux across the poles of a pick-up coil. The impulse wheel will be understood to bemounted on the same shaft with the distributor whose phase is to be maintained in synchronism with the incoming signals.

Fig. 6 shows times of charging a `condenser CI2 as controlled by ignition periods of a gaseous discharge tube V4 and an extinction period of a second gaseous discharge tube V6, which is disposed in back-to-back relationship with the flrst tube. The condenser charge serves the purpose of measuring the front half of a marking signal of dot unit length,

Fig. 7 shows times of charging a condenser CI3, while VII is blocked and from a reference voltage as established when VI3 strikes in response to an A-pulse. The charge on CI3 is used for measuring time intervals representing normally the trailing half of a marking signal of .dot-

unit length. As will be hereinafter explained in to be controlled in the same manner as V4 is the other will have its anode potential reduced more detail, the times measured in accordance with tire charging slopes on the curve of Fig. 6 are compared with those as measured in accordance. with the effective charging slopes on .the curve .of Fig. 7. A dierentlating device is caused to produce phase correction in accordance with this comparison.

Referring now to Fig. 1, I show therein a transformer 2 the primary of which is connected toany suitable receiving apparatus, whereby the tone frequency signals may be delivered. 'Ihe terminals of the secondary of the transformery 2 are connected to the anodes of a double-diode rectifier VI, while a center tap from the transformer secondary is connected across 'a resistor RII to the grounded cathode of VI. A capacitor C4 is used to absorb the ripple component of the rectified wave energy. When VI rectifles the signaling energy as during a marking impulse, V2,l

which normally operates at zero grid bias, is blocked by the signal and remains blocked for the duration of each marking element; A signal threshold is established by a normally slightly positive bias on V2 produced by means of re sistors R25,4 RI2, RI3 and RI4, which inA combination constitute a voltage divider between the mally held at a negative bias from the' -C source terminal, being connected thereto through RII and Re.

Another gaseous tube VI 2 has its control grid connected through R2I to a terminal of C l so as,

to a sufilciently low value to produce extinction of the previously maintained discharge therein.

VID is a diode rectifier the anode of which is connected through R20 and RIS to the +B source terminal. The cathode of VIIl is connected through a resistor R22 to the anode of V l2 and is also directly connected to a terminal of CI2. CI2 is acapacitor which is used to store a charge', the voltage of which rises substantially in proportion to the duration of the front end timing interval, that is, during the first half of a received marking impulse of dot unit length. This Will be explainedhereinafter when the operation of the circuit is discussed. The second time interval to be measured starts at the center of a marking impulse of dot unit length and terminates with the back edge of the marking signal. If,'however, the marking signal is of some multiple of a baud length, it is necessary to nullify the effects of false starts so that the final half -baud interval within the duration of a. marking impulse shall be the one to be compared with the front end time interval. The baud center as determined by the phase of the receiving distributor is coincident with the passage of teeth on the phonic wheel 6 in front of the magnetic pole faces of the pick-up coil 4. This relationship between the teeth of 6 and the pole faces of 4 is shown in the.drawings. The magnetic reluctance at this point is less than at other positions of the phonic wheel 6. Cbnsequently a surge impulse is developed in the pickup coil 4 which produces a voltage drop in R3 leading to ground and to the cathode of V9.

'I'he pick-up coil 4 is directly connected tothe grid of V9 and biases this tube to cut-oir. V9. as will be seen, is self-biasedv and normally draws current, its 'anode being connected to the -I-B source through R2. However, the anode of V9 is directly connected to the anode of V8, the grid of the latter being normally maintained at a zero bias so that this tube draws current ufitil the commencement of a marking impulse.

`When rectification of the marking impulse starts in VI a potential drop occurs across RII additional Vto that which is normally produced in'V is, therefore, biased to cut-oil' by the marking signal, and the plate voltage of V9 is no longer influenced by the presence of N8. This -'causes V9 to amplify the impulse from the pickup coil 4. This impulse is designated an A-pulse and is developed across C2 and R4, thus influencing the grid bias on gaseous discharge tubes V6 and VII, whose grids are connected to parallel 'storage of a charge on CII.

current flow in VIE and VI proportional to the At the commencement of the back -end integration period pick-up coil 4 kdelivers an A-pulse which is ampliiied and impressed positively across C2, and thence across R4 and R6 so as to cause VIS to strike. When V13 becomes ionized adischarge path for CI3 is obtained through this tube and Rl so as to reduce the voltage on CI3 to a reference level. This operation lasts for a negligibly small time interval and then VI@ becomes automatically, extinguished. Immediately thereafter CI3 begins to charge again through R5, R9 and the diode rectifier VII and continues to do so until VI'I is again rendered conductive by the cessation of signal rectiea.- tion in VI. A

Ifthe marking element of the signal endures for longer than one baud length, then a subsequent impulse'or impulses will be delivered by the pick-up coil 4, thus causing VI3 to repeatedly strike .and to discharge CI3 to the same reference levelat which the useful charging period is to commence.

It will be noted that the A-pulse as applied .to the grids of V0 and VI3 serves bothto terminate the front end integration period and to initiate the back end integration period. When V6 ionizes, the iiow of current through RZI and VIO ceases'because the charge alreadyy stored on CIZ renders the cathode of VIO more positive than the anode thereof. Hence the charge stored on CIZ remains until released by the momentary ionizationof VIZ at the front edge of the next of the last half-baud time interval. during a marking impulse of any length, that is, when +B potential is applied across R5, R9 .and through VII to CI3. The cancellation of charges on CI3 prior ,to the final charge within a prolonged marking period is shown bythe back edges U of certain voltage peaks indica in Fig.' 7.

Differentiation between the charges on CIZ and CI3 respectively is manifested by means of two triode tubes VI4 and VI 5.

A connection is'provided from the mid-tap on the secondary of transformer 2 to a potentiometer R25 and thence through resistors R24 and R20 to the grids of tubes VI4 and VI5 respectively. The potentiometer R25 has one terminal connected to the .-C potential source and its tap is adjustable t'o render the grids of VI4 and VI5 .more orless negative, as required, with re- ,spect to their cathodes. When VI rectiiies the marking signal veltage,l however, the increased potential drop across RII biases the grids of VI4'v and VI 5 below cut-olf, s o that these tubes cannot conduct during a niarking signal. During a spacins sisnal the grid vpoinmtials on vu 'andA VIS are respectively influenced by the charges on CIZ and CI3', since CIZ produces a potential drop acro R23 andRZlwhich is greater or less than the potential drop produced by CII,across condenser charges.

The tubes VIIl and VIS are arranged in a differential circuit relationship, them anodes be- R38, R39 and R40 between the +B source and v cillatory current is setup. Therefore, a voltage of substantially sine wave; formation appears the anode of VI4; it also includes R4I', REZ and R43 in the anode circuit .of VI 5. The relative conductivity across these two anode circuit paths determines the DC bias potential as applied to the grid of V3 with respect to its cathode. This is true because R40 and R43 constitute bias resistors in the input circuit of V3, and a grid biasing source 5I is inserted in series between the grid and cathode. an independent anode potential source 50, the anode circuit including a choke L.

When the phase of the receiving distributor lags with respect to the incoming signals. the time interval measured between M and A, as indicated by the charge on CIZ, causes VI4 to conduct at a higher rate than VI5. This renders the bias on'V3 more negative than normally. The effective resistanceof V3', therefore, in

creases and produces a change in the eectiveshunt path across the tank circuit 22. 'I'his tank circuit is constituted as part of the frequency control circuit for an oscillator V5. "The frequency of V5 is increased by this action upon the tank circuit 22, thus speeding up the oscillator and correcting the phaseof receiving distributor.

'Because V5 is self-biased there will be no bias when the circuit is first turned on. Therefore, a pulse o'f plate current will flow in V23. This pulse is fed. to VIS which amplifles and limits its amplitude as well as introducing a phase shift of substantially- 180. This amplified, inverted pulse is fed back to the tank Z2, in which anosacross the tank. This vbltage initiates anotherl change of current in V5'and the cycle is repeated.

The oscillator V5 has la `grid-to-cathgide cir'- cui't which includes potentiometer 54 and resis tor 55. CIB isin shunt with resistor 55. Amplifier tube V'I has its cathode connectedito the vcathode'of V5. V1 possesses a control grid circuit which includes a tap on potentiometer 54.

value .by means of the adjustable tap on potentiometer 54. v'I'he output circuit of V1 includes which is suitable for distributor phase correo. tion purposes. The details of such a utilization4 me and R21. It will thusbe seen that durim; spacing'intervals the charges stored on CI2 and CI3 in combination with .the normal negative bias potential applied'to the grldsof VI4 and 'potential source 52.

circuit are not herein shown, since they form no part of the` present invention. Reference is made, however, toV U. S. Patent No..1,'14'1,24 8,4 granted February 18, 1930, to W. A. Knoop for 1 disclosure of means controlled by an oscillator for adjusting the phase of a distributorto syn@v signals.

Vlijthrough R24- and R20, result in a control 01. 75 coextensive with the period between the front 'I'his tube is provided with and back edges of a marking signal, means for producing a second control condition coextensive in time with a subsequent spacing signal, means for producing a periodic local impulse at the instant when the rotative element of said distributor crosses a reference meridian designated as the baud center, means operative during said iirst control condition for storing a capacitive charge commensurate with the time interval from the front edge of a marking signal to the next succeeding local impulse, means for storing a second capacitive charge commensurate with the time interval commencing with a local impulse next preceding the back edge of a marking signal and ending with the arrival of said back edge, means operative during said second control condition for comparing the iirst and second capacitive charges, an oscillator having a phase correcting function, and meansfor varying the fresignals `of 'baud length and multiples thereof, means for generating periodic timing impulses having a substantially constantphase relation to the operation of said oscillator, a 'frequency control-circuit arrangement coupled to said oscillator, a pair of interval timing devices included in said control circuit arrangement, one of said timing devices being operative to .measure an interval which starts atfthe iront edge of .a marking vsignal andends at the ilrst baud center within said marking signal, the other of said timing devices being operative to measure an interval which starts vat a baud center next preceding the back edge of said marking signal and ends"at said back edge, each of said baud centers being determined by said means for generating periodic timing impulses, and means in said frequency control circuit arrangement for diierentiating between the time intervals measured by the two timing devices respectively, the last said means being operative only during the reception of spacing signals. y

4. Ina system for synchronizing an oscillato with a series of incoming signals whose baudpulses, means for causing one of said capacitors to accumulate a charge commencing vat-the trant edge oi.' a markingl signal, to cease charging in response to the next ensuing periodic pulse, and to store said charge until the arrival of the front edge of a next subsequent marking signal, means for causing the other of saldcapacitors to repeatedly accumulate charges starting from a reference voltage in response to each ampliiied pulse, to cease charging on arrival of the back edge of a marking signal and to store said charge through the period of a subsequent spacing signal, an oscillator for controlling the phase of said distributor, and means operative during the period of said spacing signal for controlling the frequency oi said oscillator in dependence upon the relative voltages of the two charges thus capacitively stored.

3. In a synchronizing system, cyclically opery able receiving apparatus including an oscillator the frequency of which is to be maintained in phase agreement with the reception` of incoming unit lengths are commensurate with half cycles of said oscillator, means including two capacitors for storing comparable corrective charges, said capacitors having means connected thereto for 'respectively integrating a front-end period and a back-end period of each marking signal, the two said periods combined being equal to a baud,

,means operable during reception of a spacing signal for diierentiating between said corrective charges, and means responsive to the dierentiating means for varying the frequency of said oscillator, thereby to maintain the desired synchronism with the incoming signals.

5. A system in accordance with claim 4 and including means effective upon that one of said A capacitors which integrates thecback-end period for repeatedly discharging the same to a reference voltage until a baud center is reached which next precedes the back edge of the marking signal. 

